Electric cartridge fuse with external solder joints

ABSTRACT

A cartridge fuse with &#39;&#39;&#39;&#39;exposed&#39;&#39;&#39;&#39; solder joints conductively interconnecting the fusible element means and the terminal caps on the casing of the fuse (as distinguished from a cartridge fuse having &#39;&#39;&#39;&#39;blind&#39;&#39;&#39;&#39; solder joints serving the same purpose) is provided with a novel kind of &#39;&#39;&#39;&#39;exposed&#39;&#39;&#39;&#39; solder joints. The axially outer ends of the fusible element means are clamped between the outer surface of the casing and the inner lateral surfaces of the terminal caps. The lateral surfaces of the terminal caps have apertures in registry with the ends of the fusible element means. The apertures form cavities for solder joints conductively connecting the ends of the fusible element means and the terminal caps.

United States Patent Kozacka [451 Sept. 12, 1972 [541 ELECTRIC CARTRIDGE FUSE WITH 2,143,038 1/1939 Smith, Jr. ..337/231 EXTERNAL SOLDER JOINTS 72 I t Fad i Primary Examiner-Bernard A. Gilheany 1 men or ton J Komka South Hamp Assistant Examiner-Dewitt M. Morgan Attorney-Erwin Salzer [73] Assrgnee: The Chase-Shawmut Company,

Newburyport, Mass- 57 ABSTRACT [22] Filed: P" 1971 A cartridge fuse with exposed solder joints conduc- 2 o tively interconnecting the fusible element means and the terminal caps on the casing of the fuse (as distinguished from a cartridge fuse having blind solder iii-2.8L ..337/2ii2613h3;/s2/i joints serving the same purpose is provided with a o 00 l k d f s d" r m Th [58] Field of Search ..37/159, 162, 163, 166, 185, m C am y outer ends of the fusible element means are clamped 37/228, 231, 232, 234, 237, 248, 251, 252, between the outer surface of the casing and the inner 292 lateral surfaces of the terminal caps. The lateral sur faces of the terminal caps have apertures in registry [56] References cued v with the ends of the fusible element means. The aper- UNITED STATES PATENTS tures form cavities for solder joints conductively connecting the ends of the fusible element means and the 2,680,173 6/1954 Hitchcock ..'..337/25l X terminal caps 1,228,354 5/1917 Young ..337/232 3,094,600 6/1963 Kozocka ..337/232 7 Claims, 5 Drawing Figures PAIENIEUSEP I 2 I972 FIG. 2

FIG.I

FIG.4

INVENTORI ATTY.

ELECTRIC CARTRIDGE FUSE WITH EXTERNAL SOLDER JOINTS BACKGROUND OF THE INVENTION solder joints. No entirely satisfactory solder joint of the O exposed variety has been evolved as yet. All blind solder joints are subject to the limitation of not allowing visual inspection without destruction of the particular fuse.

U.S. Pat. No. 3,425,0l8'to Frederick J. Kozacka, Jan. 28, 1969 for MINIATURIZED TIME-LAG CAR- TRIDGE FUSE HAVING RIBBON-TYPE FUSE LINK shows a fuse having a type of exposed solder joint which is widely applied in the fuse art. The end surfaces of the terminal caps are perforated for threading the ends of the fuse link through the perforations from the inside of the casing to the outside thereof. The ends of the fuse link outside of the casing projecting through the perforations in the caps are conductively connected to the caps by means of external solder joints. This design is subject to two important limitations. It does not lend itself to relatively high current ratings because in such instances there is a danger of melting of the solder and subsequent blowout of the latter by pressure generated inside of the casing of the fuse incident to blowing thereof. It is desirable to maintain pressure between the end of a fuse link and a terminal cap while soldering the former to the latter. This is not feasible with the structure of U.S. Pat. No. 3,425,018, and this is the second significant limitation to which this structure is subject. It is, therefore, a principal object of this invention to provide electric cartridge fus'es of the exposed solder joint variety which, fuses are not subject to the aforementioned limitations.

Another object of the invention is to provide cartridge fuses similar to those disclosed in U.S. Pat. No. 2,680,173 to Paul C. Hitchcock, June 1, 1954 for ELECTRIC FUSE, but not subject to the drawbacks inherent in the structures disclosed in that patent.

The above patent refers to cartridge fuses having fusible elements whose ends are bent around the edges formed by the ends of the tubular casings, engage the outer surface of the casings and are clamped by terminal caps or ferrules against the outer surface of the casings. The ends of the fusible elements project beyond the axially inner edges of the terminal caps or ferrules, and are bent 180 around said edges, and spotwelded to the outer surfaces of the terminal caps or ferrules.

Fuses of the above description do not perform consistently, i.e. the time-current curves thereof are very wide bands rather than very narrow bands, or quasi lines. I have found that the reason attributable to this fact resides in variations of the quality of the contact prevailing between the fusible element and the terminal caps or ferrules. There is a minimum of contact resistance between the terminal caps or ferrules and the fusible element at the point where the latter is spotwelded to the former. The contact resistance between the terminal caps and the fusible elements is undetermined and uncontrollable for that portion of the fusible elements which is situated between the points where the fusible elements are bent around the edges of the casing and the points where the fusible elements are spot-welded to the terminal caps. This contact resistance is undetermined and uncontrollable since it depends inter alia upon the condition of the surface of the above referred-to portions of the fusible elements and the pressure prevailing between these portions and the terminal caps, and since these two factors are undetermined and uncontrollable.

As a result of the above conditions, samples of apparently identical fuses embodying the teachings of U.S. Pat. No. 2,680,173 behave as if the length of the fusible elements thereof were subject to significant variations.

SUMMARY OF THE INVENTION In fuses embodying this invention the fusible element is bent around the edges of a tubular casing and clamped between the outer surface of the casing and the inner surface of a terminal cap or ferrule in a way similar to that disclosed in the above U.S. Pat. No. 2,680,173. Each of the pair of terminal caps has an aperture in the lateral surface thereof arranged opposite to one of the ends of the fusible element. A solder joint conductively connecting one of the ends of the fusible element to one of said pair of terminal caps is arranged substantially inside each aperture of said pair of terminal caps.

This reduces drastically the length of the portion of the fusible element along which the contact resistance between it and a terminal cap is variable and uncontrollable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is partly a side elevation of a fuse embodying this invention and partly a longitudinal section of such a fuse taken substantially along I-I of F IG.2;

FIG. 2 is in substance a top plan view of the structure of FIG. 1 showing the end surface of the terminal cap as being partly broken away and the lateral surface of the terminal cap sectioned by a horizontal plane;

FIG. 3 is a side elevation of the top end of the structure of FIG. 1 as seen from right to left;

FIG. 4 is an exploded top-plan view of a detail of the structure of F 16.1; and

FIG. 5 is a portion of FIG. 1 drawn on a larger scale than FIG.1.

'- DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings, numeral 1 has been applied to indicate a tubular main casing of electric insulating material, eg fiber or glass-cloth melamine. Casing 1 is closed on the ends thereof by terminal caps or ferrules 2, each provided with a knife blade contact 2a. The axially inner edges 3 of terminal caps 2 are crimped into casing l. Sub-casing 4 is arranged inside of main casing 1 in coaxial relation to the latter. The outer diameter of sub-casing 4 is substantially less than the inner diameter of main casing 1. Therefore a toroidal gap is formed between main casing l and subcasing 4. The upper portion of sub-casing 4 is provided with a liner 4 of insulating material forming an upper shoulder 4". A like shoulder is formed by liner 4' substantially midway between the ends of sub-casing 4.

The sub-housing 4 houses two spring-biased parts 6 and 7 of which the formed is substantially in the shape of a plunger and the latter substantially in the shape of a bell, or inverted pot. The upper end surface of part 7 forms an annular flange and helical spring 8 rests with the upper end thereof against that flange. The lower end of helical spring 8 rests against a flange integral with plunger 6 inside of bell-shaped member 7. Member 7 is also provided with a radially outwardly projecting flange 7a abutting against the lower rim or circular edge of sub-housing 4. The bottom of member 7 is closed by a disc-shaped cover plate 13 of metal and the axially inner end of fusible element or ribbon fuse link 9" is soldered at 7 to cover plate 13 by a soft solder having a relatively high fusing point. Reference character 6 has been applied to indicate two solder joints formed by soft solder having a relatively low fusing point. One of these two solder joints conductively interconnects parts 6 and 7, and the other of these two solder joints conductively interconnects plunger 6 and the axially inner end of a fusible element or ribbon fuse link 9'. Fusible element sections 9 and 9" are perforated copper ribbons as clearly shown in FIG. 3 wherein reference character 14 has been applied to indicate perforations in fusible element or fuse link 9.

The upper end of sub-housing 4 is closed by a pair of circular discs a,5b of electric insulating material of which the lower disc 51) rests against shoulder 4" and the upper disc 50 rests upon lower disc 5b. As seen in FIG. 4 the juxtaposed sides of discs 5a, 5b are provided with rectangular cut-outs. When discs 511,511 are superimposed in registry these rectangular cut-outs define a narrow slit allowing the passage of fuse link section 9 from the space within sub-casing 4 to the space outside sub-casing 4 and within main casing 1.

The ends of fuse link sections 9' ,9" immediately adjacent sub-casing 4 extend along the axis of main casing 1. Each fusible element section 9',9" has a first bend inside of main casing 1, and a second bend coextensive with one of the rims of main casing 1. The axially outer ends of fusible element means 9',9" are sandwiched between the outer surface of casing l and the radially inner surfaces of caps 2. Each of caps 2 has a circular aperture 20 in the lateral surface thereof arranged opposite to, or in registry with, one of the ends of fusible element means 9,9". A solder joint 11 is arranged inside each of the circular apertures 20 in caps 2, each solder joint 11 conductively connecting the axially outer end of one of fuse links 9,9" to one of terminal caps 2. The radially outer surface of each solder joint 11 is covered with a heat resistant protective layer 12 to avoid exposure thereof to the effects of ambient atmospheres. Protective layer 12 may be formed by silicone grease.

Sub-casing 4 is surrounded by a body of pulverulent arc-quenching filler embedding fusible element sections 9',9" and filling main casing 1. Discs 5a,5b preclude arc-quenching filler 10 from penetrating into sub-casing 4 where its presence is not desired. Discs 5a,5b may be held in position by friction.Upon filling main casing l with filler 10 the latter tends to maintain discs 5a,5b in proper position.

On occurrence of protracted overloads solder joint 6' soften and plunger 6 moves under the action of spring 8 away from the axially inner end of fusible element 9'. Thus an arc is kindled which is confined to a chamber formed by sub-casing 4. This chamber does not contain any pulverulent arc-quenching filler whose properties are not compatible with the interrupting requirements for low current arcs. Thus parts 4,4,5a ,5b,6,7,8 and 13 form an effective overload interrupting device.

The ribbon fuse link sections 9',9" are a means for interrupting major fault currents, such as short-circuit currents.

The aforementioned overload interrupting device 4,4,5a,5b,6,7,8 and 13 and the two ribbon fuse link sections 9',9" connected in series with that device form a self-contained substantially C-shaped sub-assembly which has the configuration shown in FIG. 1 before being mounted inside of main casing 1. To form such a self-contained and self-supporting sub-assembly ribbon fuse link sections 9,9" must be sufficiently stiff to retain without support any shape imparted to them, and more particularly the shape shown in F101. It is apparent from FIG. 1 that each fuse link section 9',9 includes an inner end and an outer end both parallel to the axis of main casing l. The intermediate portions of fuse link sections 9',9 are diverging radially outwardly and the aforementioned sub-assembly forms a clip-on unit that can readily be affixed to casing 1, thus greatly reducing the cost of, and the amount of time involved in, production of the fuse.

It will be apparent from FIG. 5 that the axially outer end of fuse link 9' is clamped between end surface 2b of cap 2 and the rim of casing 1. Thus pressure generated inside of casing l is sealed off and cannot act upon solder joint 11 and blow out the latter.

I claim as my invention:

1. An electric cartridge fuse including a; a tubular casing of insulating material;

b. a fusible element inside said casing having an end bent around the rim formed by one of the axially outer ends of said casing and engaging the outer surface of said casing;

c. a terminal cap provided with a blade contact on one of the end surfaces thereof and mounted on said one of the axially outer ends of said casing upon said bent end of said fusible element, said cap having an aperture in the lateral wall thereof arranged substantially in registry with said bent end of said fusible element; and

. a body of soft solder inside said aperture of said cap conductively interconnecting said bent end of said fusible element and said cap.

2. An electric cartridge fuse as specified in claim 1 including a protective layer against adverse effects of ambient atmosphere superimposed upon said body of soft solder.

3. An electric cartridge fuse as specified in claim 2 wherein said protective layer is formed by silicone grease.

4. An electric cartridge fuse including a. a tubular casing of electric insulating material;

b. fusible element means arranged inside of said casing and having ends bent around the rims formed by the axially outer ends of said casing, said ends engaging the outer surface of said casing;

c. a pulverulent arc-quenching filler inside of said casing submersing at least a portion of said fusible element means;

d. a pair of terminal caps mounted upon the axially outer ends of said casing and each provided with a blade contact extending in a direction longitudinally of said casing, said ends of said fusible element means being sandwiched between the outer surface of said casing and the radially inner surface of said pair of caps, each of said pair of caps having an aperture in the lateral surface thereof arranged opposite to one of said ends of said fusible element means; and

e. a pair of solder joints each arranged substantially inside of said aperture of one of said pair of caps and each conductively connecting one of said ends of said fusible element means to one of said pair of caps.

5. An electric cartridge fuse as specified in claim 4 wherein the radially outer surfaces of said pair of solder joints are covered by heat-resistant protective layers to avoid exposure thereof to the effects of ambient atmosphere.

6. An electric cartridge fuse as specified in claim 5 wherein said protective layers are formed by silicone grease.

7. An electric cartridge fuse including a. a tubular casing of electric insulating material;

b. a spring-biased overload current interrupting device arranged inside said casing and including solder joint means normally maintaining said device in position against the spring bias thereof;

. a pair of fusible elements inside said casing, said pair of fusible elements including axially inner portions conductively connected to said current interrupting device and axially outer portions enclosing acute angles with said axially inner portions, said axially outer portions having ends bent around the rims formed by the axially outer ends of said casing and engaging the outer surface of said casing;

. a pair of terminal caps mounted upon the axially a pair of solder joints each arranged substantially inside of said aperture of one of said pair of caps and each conductively connecting one of said ends of said axially outer portions of said pair of fusible elements to one of said pair of caps. 

1. An electric cartridge fuse including a. a tubular casing of insulating material; b. a fusible element inside said casing having an end bent around the rim formed by one of the axially outer ends of said casing and engaging the outer surface of said casing; c. a terminal cap provided with a blade contact on one of the end surfaces thereof and mounted on said one of the axially outer ends of said casing upon said bent end of said fusible element, said cap having an aperture in the lateral wall thereof arranged substantially in registry with said bent end of said fusible element; and d. a body of soft solder inside said aperture of said cap conductively interconnecting said bent end of said fusible element and said cap.
 2. An electric cartridge fuse as specified in claim 1 including a protective layer against adverse effects of ambient atmosphere superimposed upon said body of soft solder.
 3. An electric cartridge fuse as specified in claim 2 wherein said protective layer is formed by silicone grease.
 4. An electric cartridge fuse including a. a tubular casing of electric insulating material; b. fusible element means arranged inside of said casing and having ends bent around the rims formed by the axially outer ends of said casing, said ends engaging the outer surface of said casing; c. a pulverulent arc-quenching filler inside of said casing submersing at least a portion of said fusible element means; d. a pair of terminal caps mounted upon the axially outer ends of said casing and each provided with a blade contact extending in a direction longitudinally of said casing, said ends of said fusible element means being sandwiched between the outer surface of said casing and the radially inner surface of said pair of caps, each of said pair of caps having an aperture in the lateral surface thereof arranged opposite to one of said ends of said fusible element means; and e. a pair of solder joints each arranged substantially inside of said aperture of one of said pair of caps and each conductively connecting one of said ends of said fusible element means to one of said pair of caps.
 5. An electric cartridge fuse as specified in claim 4 wherein the radially outer surfaces of said pair of solder joints are covered by heat-resistant protective layers to avoid exposure thereof to the effects of ambient atmosphere.
 6. An electric cartridge fuse as specified in claim 5 wherein said protective layers are formed by silicone grease.
 7. An electric cartridge fuse including a. a tubular casing of electric insulating material; b. a spring-biased overload current interrupting device arranged inside said casing and including solder joint means normally maintaining said device in position against the spring bias thereof; c. a pair of fusible elements inside said casing, said pair of fusible elements including axially inner portions conductively connected to said current interrupting device and axially outer portions enclosing acute angles with said axially inner portions, said axially outer portions having ends bent around the rims formed by the axially outer ends of said casing and engaging the outer surface of said casing; d. a pair of terminal caps mounted upon the axially outer ends of said casing, and each provided with a blade contact extending in a direction longitudinally of said casing, said ends of said axially outer portions of said pair of fusible elements being sandwiched between the outer surface of said casing and the radially inner surfaces of said pair of caps, each of said pair of caps having an aperture in the lateral surface thereof in registry with one of said ends of said axially outer portions of said pair of fusible elements; and e. a pair of solder joints each arranged substantially inside of said aperture of one of said pair of caps and each conductively connecting one of said ends of said axially outer portions of said pair of fusible elements to one of said pair of caps. 